Timer-counter apparatus is well known in the prior art and is utilized to measure the voltage-time characteristics of applied unknown signals which vary periodically as a function of time. These signals provide information useful in many applications. For example, speed, phase, revolutions per minute, frequency and the like may be ascertained therefrom. Such is normally accomplished in timer-counters by measuring the frequency of the occurrence of the electrical signal applied, the period of elapsed time between certain electrical events as they occur and the time displacement between two predetermined points on a particular electrical signal as applied.
To accurately measure these events, or elapsed time, requires an accurate setting within the instrument of a reference level against which the input signal may be compared to thereby provide an output or trigger signal when the input wave form achieves a predetermined relationship with the reference level.
In the prior art, to properly ascertain the position where the reference level was to be set required users of the instruments to make measurements with external equipment such as voltmeters or oscilloscopes to ascertain generally the appearance of the input wave form and its general value before the timer-counter instrument could in fact be used. As an alternative, the users of the prior art instruments could "hunt" with the reference level setting controls on the instruments and periodically make measurements with the instruments to obtain such generalized information.
Obviously such prior art techniques require the utilization of additional instruments and consume additional operator time, both of which are extremely expensive, unnecessary and often lead to operator error.